Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: IFR 1200S Jumping Frequency  (Read 3884 times)
K4JJL
Member

Posts: 836




Ignore
« on: May 17, 2016, 04:22:19 PM »

Powered up my IFR service monitor and when generating, the frequency jumps 1k roughly every 1 second. Also, when generating audio through the "tone out" jack, I see a small ever-so-slight warbly phase shift. I'm thinking power supply ripple. Any ideas where to start looking? 
Logged
K5LXP
Member

Posts: 5346


WWW

Ignore
« Reply #1 on: May 17, 2016, 05:34:59 PM »


How old is it?  I have a stabilock service monitor, circa 1991.  A good number of the electrolytic caps in it had leaked, and who knows if the rest still behave like capacitors.  So your notion of ripple is a possibility if your IFR is older.  One subassembly at a time I'm R&Ring every single cap, 209 of them.  Some had been leaking long enough the electrolyte has eaten some of the PCB traces and damaged surrounding components, so it remains to be seen if it will work again after this effort.  Might be worth a peek inside the IFR and see how the caps look.

Mark K5LXP
Albuquerque, NM

Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #2 on: May 18, 2016, 08:42:55 AM »

I was thinking the same thing.  I've repaired tons of Spectras and TVs (and even my old Sega Game Gear) that had the same issues.  I was hoping to narrow it down to one board initially.  I just tried running it on DC and still does the same thing.  I'm going to assume the power supply is ok now.

I suppose the first board I'll pull and shotgun will be the synthesizer board.  Thank goodness the service manual is on Repeater Builder.
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #3 on: May 20, 2016, 05:32:38 AM »

Pulled several boards last night. Caps look spotless. None of the PLL unlock LEDs came on. Seems like it might be a VCO issue. The signal generated by DUPLEX jack is rock solid, but the signal generated by the T/R jack is changing approximately 1k every 1 second up and down at a steady rate. I can't get to the steering voltage because it's all inside coax with connectors I don't have adapters for. I'll shoot an email to KG and see if I can pick his brain.
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #4 on: May 20, 2016, 08:31:30 AM »

Here's a video of the issue.

https://www.youtube.com/watch?v=OrlWU8UsveY
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #5 on: May 23, 2016, 08:47:56 AM »

Narrowed it down to the fast low loop board.  Apparently it's a known issue covered under a technical bulletin from IFR.  Anybody have any suggestions on where to look on this board?
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #6 on: May 26, 2016, 10:03:57 AM »

Found the 18.8 MHz oscillator going crazy.  Steering voltage running the tuning varactor was varying up and down.
Logged
WA2ISE
Member

Posts: 1057




Ignore
« Reply #7 on: May 26, 2016, 11:52:14 AM »

Steering voltage running the tuning varactor was varying up and down.

Could be something in the loop filter, phase detector, or the 18.8MHz oscillator itself.  As a test, try feeding the varactor diode with a steady fixed voltage, and see if the steering voltage still varies.  And see if the oscillator is steady or not.  Idea is to divide and conquer, hunting for the defective circuit.  
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #8 on: May 26, 2016, 12:47:43 PM »

I think it's a tantalum cap shorting out inside, a zener that's supposed to hold 6.9v is only at 6v, or the varactor itself.  I've ordered the zener and varactor.  I have bags of caps at the house.  I'll probably lift a leg on the cap to see if the voltage goes back up.
Logged
K4JJL
Member

Posts: 836




Ignore
« Reply #9 on: November 21, 2017, 12:02:16 PM »

Just so this isn't left open ended, here's what I fixed...



And here's the locations on the board...

Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!